The invention relates to a novel type of molding element intended to be fitted in a mold for molding a cutout in a rubber tread intended, for example, for a tire; the invention also relates to molds equipped with this type of molding element.
In FR 2 759 321, there is proposed a mold for molding a tread of a tire, this tread comprising a tread pattern provided with incisions, the main walls defining the incisions being connected by at least one connecting bridge so as to maintain a satisfactory level of rigidity for said tread. The mold described in this application is formed of two parts which come into contact with each other in the molding position and each part bears at least one molding element for molding, an incision. In the molding configuration, certain of said molding elements of one mold part are in contact with certain molding elements of the other mold part, their end walls cooperating to form orifices intended to allow the rubber to pass during molding and thus to mold the bridges connecting the walls of the incision. After molding, it is possible to open the two mold parts without breaking said rubber bridges.
Although this technique does make it possible to produce connecting elements between the walls of a cutout, it however requires manufacturing the tread separately before assembling it with suitable means on a tire without a tread to finish the manufacture of said tire. An additional operation is then necessary to join the tread to the tire thus covered. It is therefore costly owing to the large number of operations, and requires very special attention in the transport and assembly phases for forming the tire.
In another French application, 98-08653, there was proposed a molding element for molding a rubber block in a tread, the lateral surface of said block being connected to the tread by at least one rubber connecting bridge. This molding element comprises molding blades mounted on a head which can turn about an axis substantially parallel to the direction of molding/demolding of the mold part equipped with said molding element. To obtain connecting bridges connecting the walls of the rubber block, it was proposed, for example, to arrange two series of blades on two concentric cylinders, each blade of a cylinder being crossed and in contact with blades of the other cylinder so as to define, in the molding configuration, orifices permitting the molding of said bridges. During the demolding under the action of the displacement of the mold part bearing this molding element, the vulcanized rubber exerts contact actions which force the cylinders bearing the blades to turn relative to each other. This process. notwithstanding that it is highly advantageous and achieves high-performance, once the number of molding elements becomes very large, requires a very great demolding force which increases the complexity of production of the apparatus in displacing the mold parts during the demolding operation.
This problem is furthermore a general problem which arises when the number of molding elements becomes very large, whatever their structure (this is a current tendency in all categories of tires for passenger vehicles or heavy vehicles).